Oxygen uptake efficiency slope at anaerobic threshold can predict peak VO2 in adult congenital heart disease

Abstract

Introduction

Assessment of exercise capacity by cardiopulmonary exercise testing (CPET) in adults with congenital heart disease (CHD) is important for prognostication and preoperative assessment. Peak oxygen uptake (PVO₂) is used commonly, but can be challenging due to the difficulties of undertaking maximal CPET testing in this population. We explored whether oxygen uptake efficiency slope (OUES) at ventilatory anaerobic threshold (VAT), the point during CPET at which OUES becomes strongly correlated with PVO₂, and is more reliably available from submaximal CPET, can predict PVO₂ in adults with CHD.

Methods

We assessed consecutive individuals who completed maximal CPET at our cardiorespiratory centre, as part of routine service review, between March 2019 and August 2021, recording data such as PVO₂, VAT and OUES at various proportions of a maximal test (75 %, 90 %, 100 %, and VAT). We employed linear regression modelling to analyse the association between PVO₂ and OUES at VAT, and subsequently create an equation to predict PVO₂ from OUES at VAT. Parametric data are presented using Pearson's correlation coefficient and non-parametric data using Spearman's rho.

Results

We analysed 391 individuals (177 female, age 32 ± 11 years). Mean ± SD PVO₂ was 23.3 ± 6.86 ml/min/kg or 1724 ± 540 ml/min, peak VE 86.7 ± 25.4 l/min. The point of VAT as a percentage of PVO₂ achieved was 66.5 ± 9.4 %, and VAT as a percentage of predicted PVO₂ 46.9 ± 11.4 %. PVO₂ was correlated with OUES at 100 % (R = 0.91, P < .001), 90 % (R = 0.91, P < .001), 75 % (R = 0.89, P < .001) of maximum, and VAT (R = 0.83, P < .001). PVO₂ (ml/min) could be predicted by: (OUES at VAT)∗685.245 + (BMI [kg/m²])∗5.045 + (FEV₁ [l])∗223.620 – 153.205.

Conclusions

OUES at VAT can be used to calculate PVO₂. To our knowledge, this is the first equation using OUES at VAT to predict PVO₂ in adults with CHD. In a population who may find maximal CPET difficult, this may be a useful submaximal measurement of cardiovascular fitness, and to calculate PVO₂, which is commonly used in guideline-based decision making in CHD.